What makes a domain premium?

Trying to understand value. give me your opinions.

It must be some short catchy words, some meaningful words or some trendy words. It can be anything but short words.

Short catchy rememberable words, niche relevant terms etc.

btw sometimes non words also become premium domain.

It depends on different context. like ebola, corona etc.

I don't believe there was ever a hard definition for that. Based on what tends to do best, though, you can get a pretty good idea of what people consider a premium domain. Short domains, one-word domains, easy to spell, memorable, relevant to the current zeitgeist. I'd say those are all good qualities, premium even.
At the end of the it though though, a premium domain is only really worth what a buyer is willing to shill out (save for a trend or some fringe example where a word or phrase becomes so relevant that making a site out of it suddenly sounds like a shrewd business move. This varies wildly.) A domain that's practically worthless to one person could be extremely valuable to someone else.

Premium domains are valuable because they're easy to remember and great for branding. NakamaId has a nice selection of them.